Hi everyone! I'm having a bit of trouble with my recently acquired Apple 2 plus. When I turn it on, I get a screen full of ??@@??@@??@@. The keyboard has no effect. I tried reseating all the ROMs and spraying their sockets with contact cleaning spray but no dice. Anyone have any idea what is the issue?
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Apple ][+ Boot Issues
- Thread starter 6502Fan
- Start date
Please tell us which ROM chips you have.
Do you have all the expansion cards removed?
I would avoid using spray at this point. The only key(s) that could help at this point areare RESET and CONTROL, but that only makes sense if you have the wrong (or bad) ROM. Else at this point you could have any number of faults.
Do you have all the expansion cards removed?
I would avoid using spray at this point. The only key(s) that could help at this point areare RESET and CONTROL, but that only makes sense if you have the wrong (or bad) ROM. Else at this point you could have any number of faults.
All expansion cards are removed and reset and control have no effect.
ROM numbers are:
F8: 341-0020
F0: 341-0015
E8: 341-0014
E0: 341-0013
D8: 341-0012
D0: 341-0011
I checked with a picture of another ][+ online and they are in the right spots.
Last edited:
Ok quick thoughts on this, @@?? is alternating 00 FF in text memory so the memory is properly getting mapped to the text screen, so 1st 16k of memory is probably ok so monitor F8 ROM should be able to execute and give you a beep
and clear the screen which it is not. Problem could be a ROM, buffer IC H3,H4,H5 or ROM select IC F12. Check DC voltages on 6502 pins 2,4,6,40 should all be 5V and pin 37 around 2V ??? Of course, reseat those IC's too
Larry G
and clear the screen which it is not. Problem could be a ROM, buffer IC H3,H4,H5 or ROM select IC F12. Check DC voltages on 6502 pins 2,4,6,40 should all be 5V and pin 37 around 2V ??? Of course, reseat those IC's too
Larry G
Will do! I don't get a beep on start up.
Ok, I checked the voltages on the processor and everything is in tolerance. I also cleaned some more pins and sockets but no change. Then I left the unit on for a little while and could tell the F8 ROM wasn't getting as warm as all the others. I removed the F8 and powered the unit up, no difference. This leads me to believe the F8 ROM is bad. Another thing after leaving it on for a few minutes, when I turn it off and then back on, the ??@@s get some random characters in them. Some highlight and then dehighlight all in sync.
This sounds silly, but, put a different ROM in that socket (any of the other ROMs) and see if something else happens. It's a long shot, but having no other means of diagnostic at this point, it's something.
The test is, if you see or hear something different happen (anything), you know you have a bad F8 ROM. If nothing different ever happens, you may or may not have other problems.
You should also check some 6502 inputs, such as RESET, IRQ, and NMI. If any of those is stuck, you can narrow it from there.
You can also determine if the clock is running with a common multimeter: Phi0 should never measure 0V or 5V. It should read somewhere in between with an analog meter, and anything in the world except a steady 0V or 5V with a digital meter.
The test is, if you see or hear something different happen (anything), you know you have a bad F8 ROM. If nothing different ever happens, you may or may not have other problems.
You should also check some 6502 inputs, such as RESET, IRQ, and NMI. If any of those is stuck, you can narrow it from there.
You can also determine if the clock is running with a common multimeter: Phi0 should never measure 0V or 5V. It should read somewhere in between with an analog meter, and anything in the world except a steady 0V or 5V with a digital meter.
I swapped the ROMs, nothing new. I swapped the row of RAM, it only increased the probability of more garbage in amongst the @@??s. I also noticed the first row of chips (row A) is not getting warm at all. Could the problem lie here?
I also read on some other sites that debugging could be done with an oscilloscope. I have an oscilloscope if it comes to that.
I also read on some other sites that debugging could be done with an oscilloscope. I have an oscilloscope if it comes to that.
It's starting to sound very much like bad RAM, possibly on addition to some glue logic.
An oscilloscope is certainly useful.
At this point, if it were me, I'd replace all the RAM chips. But I usually do that anyway. Else, you could build an NOP generator and make sure address decoding is working as well as conductors.
Something that slipped my mind earlier: you have a display, so the clock must be running.
An oscilloscope is certainly useful.
At this point, if it were me, I'd replace all the RAM chips. But I usually do that anyway. Else, you could build an NOP generator and make sure address decoding is working as well as conductors.
Something that slipped my mind earlier: you have a display, so the clock must be running.
Witchy
Experienced Member
NOP generators. This reminds me that recently I've got 3 Apple ][Europlus' going again without using a generator but at least for one of the machines it would've been useful I think. However, whilst searching (again) on the best way of making one I ran across this quote that said:
"I also recommend not using one in an Apple II or any design where
*reading* memory locations can cause interesting side effects.
In Commodore hardware, you have to *write* to I/O registers to
make stuff happen; not so with the Apple. "
From here
I'm interested to know why this might be. Please feel free to tell me to create a new topic for this
W
I don't quite understand that either, but I'm not exactly an Apple hardware guru.
I do understand that some Apple I/O is triggered by address. What he means is that generally with Commodore hardware, you have I/O interfaces with registers, like the 6520/6521/6522.
I don't know what the consequences of using an NOP generator in an unexpanded Apple would be, other than the speaker buzzing. I guess I wouldn't be afraid to try it out, but maybe retrogear has better information.
I do understand that some Apple I/O is triggered by address. What he means is that generally with Commodore hardware, you have I/O interfaces with registers, like the 6520/6521/6522.
I don't know what the consequences of using an NOP generator in an unexpanded Apple would be, other than the speaker buzzing. I guess I wouldn't be afraid to try it out, but maybe retrogear has better information.
HoJoPo
Veteran Member
Some peripherals on the Apple ][ are triggered by just accessing the I/O address involved, sometimes acting as a latching toggle. So it's possible to damage some of those peripherals (disk drives, etc) by hitting the addresses that control them repeatedly, or causing them to go into an unknown state. For example, you could repeatedly force the heads on the floppy against the stop, making a lot of noise and eventually damaging the stepper motor.
A NOP generator may be OK with all the peripheral cards removed... it will hit the I/O addresses of some of the built-in hardware, but won't hurt it.
A NOP generator may be OK with all the peripheral cards removed... it will hit the I/O addresses of some of the built-in hardware, but won't hurt it.
Yes reading addresses in the I/O range of a disk controller can throw the drive out of alignment, been there, done that with some of my code experimenting years ago. Wouldn't be a problem with just the motherboard, though. I guess one thing you could try first
is verifying reset on 6502 pin 40 with your scope. It should do a momentary negative pulse when ctrl-reset is pressed.
is verifying reset on 6502 pin 40 with your scope. It should do a momentary negative pulse when ctrl-reset is pressed.
An NOP Generator causes the processor to see the value $EA in every address location. This is the instruction NOP, which the processor ignores. When it encounters that, it fetches the instruction from the next memory location.
So basically it causes your microprocessor to step through every memory location, in sequence. When it's doing that, you can easily verify the operation and connection of every address line everywhere it's supposed to go. An oscilloscope is especially handy for this.
Your best bet to build one without me trying to type it all up on this miniscule keyboard is do a search here or elsewhere on the internet. They are especially popular with the Commodore PET.
So basically it causes your microprocessor to step through every memory location, in sequence. When it's doing that, you can easily verify the operation and connection of every address line everywhere it's supposed to go. An oscilloscope is especially handy for this.
Your best bet to build one without me trying to type it all up on this miniscule keyboard is do a search here or elsewhere on the internet. They are especially popular with the Commodore PET.
Witchy
Experienced Member
Ah right, that makes sense from a peripheral point of view. I'll not be too anxious to try it next time then - I always test with no cards in anyway.
W
Witchy
Experienced Member
As KC9UDX says you have a display so the clock is running and therefore you should get around 2V on pin 37 of the 6502 (phi2). RESET on pin 40 should always be 5V while the machine's running.
Voltage-wise check for:
5V pin 8 6502
5V pin 24 ROMs
5V pin 1 4116
12V pin 8 4116
-5V pin 9 4116
You've already done the heat test. Next I'd remove all the RAM and processor to see if the display changes. With a multimeter set for continuity check that pin 2 (DI) on each *column* of RAM sockets is connected together (eg C10, D10, E10), also pin 14 (DO). Then check the address bus and CAS/RAS/WR line on each *row* (eg C3 - C10 pins 3-7 and 10-15). Google for '4116 pinout' to reference. Download the best reference guide for the ][+ from here. All the schematics you need are at the end. Another good resource is Mike Willegal's troubleshooting page here.
At its most basic you need a boot ROM (known as the $F8 autostart ROM) in F3 and Row C of RAM populated with 8 fully working chips.
W
Voltage-wise check for:
5V pin 8 6502
5V pin 24 ROMs
5V pin 1 4116
12V pin 8 4116
-5V pin 9 4116
You've already done the heat test. Next I'd remove all the RAM and processor to see if the display changes. With a multimeter set for continuity check that pin 2 (DI) on each *column* of RAM sockets is connected together (eg C10, D10, E10), also pin 14 (DO). Then check the address bus and CAS/RAS/WR line on each *row* (eg C3 - C10 pins 3-7 and 10-15). Google for '4116 pinout' to reference. Download the best reference guide for the ][+ from here. All the schematics you need are at the end. Another good resource is Mike Willegal's troubleshooting page here.
At its most basic you need a boot ROM (known as the $F8 autostart ROM) in F3 and Row C of RAM populated with 8 fully working chips.
W